A closed breeding colony of Virginia opossums is maintained to provide neonates for research purposes. Opossums are bred during the 4 month breeding season (January-April) by establishing natural matings within a group of 2-3 females to 1 male. Mortality is high among males who are killed by the females. In 1975 the conception rate was 43 percent (13 litters from 30 females). Thus far, in 2 months, 7 litters have been born to 49 females (14 percent conception rate).